No it's not unlawful but it is profane. If you are an unbeliever or are disqualified it could be lethal at least in theory.

Christians are not under law of any kind. So it isn't a question of lawfulness. The Bible does say that the person who eats unworthily eats and drinks damnation unto himself. I'm not completely sure of the meaning of this verse. Paul also says that brothers and sisters that participate even though they are not qualified to be doing so have gotten sick and died from it but aren't damned to Hell.